Surface acoustic wave device and method of manufacturing the same, IC card, and mobile electronic apparatus

ABSTRACT

A surface acoustic wave device includes a surface acoustic wave (SAW) chip and a cover that are bonded in a body by bonding a metal bonding portion of the SAW chip and a metal bonding portion of the cover and bonding extraction electrodes of the SAW chip and connection electrodes of the cover so as to hermetically seal IDT electrodes disposed on a main surface of a piezoelectric substrate of the SAW chip within a space defined between the SAW chip and the cover. The IDT electrodes and external electrodes on an upper surface of an insulating substrate of the cover are electrically connected to each other through conductive materials formed in through-holes.

RELATED APPLICATIONS

This application claims priority to Japanese Patent Application Nos.2004-366879 filed Dec. 17, 2004 and 2005-288046 filed Sep. 30, 2005which are hereby expressly incorporated by reference herein in theirentirety.

BACKGROUND

1. Technical Field

The present invention relates to a surface acoustic wave (SAW) devicesuch as a resonator, a filter, and an oscillator, and to a method ofmanufacturing the same. In addition, the present invention relates to anIC card and a mobile electronic apparatus having the SAW device.

2. Related Art

In the related art, SAW devices having SAW elements including IDTs(comb-shaped transducers: Inter Digital Transducers) constructed withalternate finger electrodes formed on a surface of a piezoelectricsubstrate and reflectors and using surface acoustic waves excited fromthe IDTs have been widely used for various electronic apparatuses. Inparticular, in addition to high frequency performance and high precisioncoping with high speed information communication, thinner SAW deviceshave been required in for small-sized, thin information apparatuses suchas IC cards.

In general, a SAW device in the related art is constructed byhermetically sealing SAW elements in a package which is formed bybonding a metal lid to a base made of a ceramic material withseam-welding. In the SAW element, bonding pads of an IDT formed on asurface of a piezoelectric substrate are electrically connected toconnection terminals of the package by using bonding wires (for example,see JP-A-2002-16476 and JP-A-2003-87072). In such a structure, thenumber of parts is quite large, and the construction is too complicated.In addition, in order to provide the bonding wires, a large space isneeded in the package, so that there is a limitation on implementing asmall-sized thin SAW device.

Therefore, there has been proposed an electronic part constructed byaccommodating the SAW device in a space formed between upper and lowercases, electrically bonding input/output electrodes of the SAW device tosecond connection members of an outer surface of the case with firstconnection members disposed in through-holes of the upper case, andsealing the through-holes with the first or second connection members(for example, see JP-A-7-86867). As a result, by simplifying the sealingstructure of the through-holes, a simple construction and a small sizecan be obtained.

In addition, there has been proposed a double layered surface acousticwave apparatus including a surface acoustic wave element having IDTelectrodes, extraction electrodes, and positive electrode bondingportions on a substrate and a cover plate constructed with a glass platehaving through-holes provided with external electrodes, wherein theextraction electrodes and the external electrodes are electricallyconnected, and wherein the cover plate and the positive bonding portionare bonded to seal the IDT electrodes (for example, see JP-A-8-213874).According to this construction, since the base and the bonding wiresmounted on the SAW element are omitted, the entire construction can besimplified, and a small-sized thin product can be obtained. In addition,production cost can be reduced, and frequency characteristics can bestabilized.

On the other hand, in order to improve a high frequency performance ofthe SAW device, spaces between the alternate finger electrodes must beshortened. In addition, if extrinsic material such as electrode materialdebris generated during manufacturing processes remains in the spacebetween alternate finger electrodes, a short-circuit may occur. In orderto solve this problem, there has been proposed a SAW apparatus capableof preventing short-circuiting between the electrodes without a decreasein Q value by forming a protective film constructed with an oxide film(alumina) with a positive electrode oxidation processes on a surface ofan IDT (for example,see JP-A-8-130433).

In the double-layered SAW apparatus disclosed in JP-A-8-213874, the SAWelement and the cover plate are bonded by aligning and closely adheringthe extraction electrodes and the through-holes at the positiveelectrode bonding portion, and thereafter, the external electrodes areformed at the through-holes and peripheral portions thereof and areelectrically connected to the excitation source by using a sputteringprocess in a vacuum. In general, since the extraction electrodes aremade of aluminum, the surface thereof is naturally oxidized due to aircontact. Therefore, after the positive electrode bonding between the SAWelement and the cover plate, although the external electrodes are formedin a vacuum, sufficient electrical conduction to the extractionelectrodes cannot be ensured.

In addition, the sealing of the through-holes is performed by formingthe extraction electrodes and the electrode of the positive electrodebonding portion with the same film thickness so as not to generate gapsbetween the extraction electrodes and the through-holes and forming theexternal extrudes on inner sides of the through-holes. However, inpractice, it is difficult to surely hermetically seal the gaps betweenthe inner side openings of the through-holes and the extractionelectrodes with the electrode films by using the sputtering process.

In addition, since the double-layered SAW device is a surface mountingtype, the external electrodes formed on a surface of the cover plate aredirectly adhered on a surface of a print board or the like with asolder, an adhesive, or the like. However, as the size of the device issmaller and smaller, the mounting area is reduced. Therefore, it may bedifficult to mount the SAW device in a good state and obtain sufficientadhesive strength after the mounting thereof, so that sufficientmechanical strength against an external force such as bending cannot besecured.

SUMMARY

In view of the foregoing, it is an advantage of the invention to providea double-layered SAW device capable of directly bonding a SAW chip and acover to seal IDT electrodes or the like formed on a surface of the SAWchip and electrically connecting the IDT electrodes and externalelectrodes on a surface of the cover through through-holes formed in thecover, thereby obtaining a thin product, securing electrical conductionbetween the IDT electrodes and the external electrodes, and securelyhermetically sealing the through-holes.

It is another advantage of the invention to provide a double-layered SAWdevice capable of preventing short-circuiting of IDT electrodes toimprove reliability, securing resonance characteristics, and obtaining athin product.

It is still another advantage of the invention to provide adouble-layered SAW device capable of obtaining a good mounting stateeven in a small-sized thin product and securing sufficient mechanicalstrength against bending after the mounting thereof.

It is still another advantage of the invention to provide a method ofmanufacturing a double-layered SAW device, and particularly, a method ofdouble-layered SAW device capable of improving mass productivity.

According to an aspect of the invention, there is provided a surfaceacoustic wave device comprising: a SAW chip having IDT electrodesdisposed on a main surface of a piezoelectric substrate, extractionelectrodes extracted from the IDT electrodes, and a metal bondingportion disposed along the entire periphery of the main surface of thepiezoelectric substrate; and a cover having through-holes disposed on aninsulating substrate at positions corresponding to the extractionelectrodes of the SAW chip, a metal bonding portion disposed along theentire periphery of a lower surface of the insulating substrate,connection electrodes disposed on the lower surface of the insulatingsubstrate along circumferences of openings of the through-holes, andexternal electrodes disposed on an upper surface of the insulatingsubstrate in peripheries of openings of the through-holes; wherein theSAW chip and the cover are bonded in a body by bonding the metal bondingportion of the SAW chip and the metal bonding portion of the cover andbonding the extraction electrodes of the SAW chip and the connectionelectrodes of the cover so as to hermetically seal the IDT electrodeswithin a space defined between the SAW chip and the cover, and whereinthe IDT electrodes and the external electrodes are electricallyconnected to each other through conductive materials formed in thethrough-holes.

In the double-layered SAW device, by bonding the connection electrodesdisposed in the peripheries of the openings of the through-holes forelectrode extraction disposed in the cover and the extraction electrodesof the SAW chip as well as by bonding the metal bonding portionsdisposed in peripheries of the SAW chip and the cover, it is possible tosecure electrical conduction between the IDT electrodes and the externalelectrodes and to more securely hermetically seal the interior of theSAW device. As a result, it is possible to implement a small-sized thinSAW device and to improve stability of operations and frequencycharacteristics.

In the above aspect of the invention, the thickness of the metal bondingportion of the SAW chip. and the metal bonding portion of the cover inthe bonded state and the thickness of the extraction electrodes of theSAW device and the connection electrodes of the cover in the bondedstate may be determined to be larger than the thickness of the IDTelectrodes. Therefore, the space between the SAW chip and the cover canbe larger than the thickness of the IDT electrodes, and the gap betweenthe IDT electrode and the cover can be secured. As a result, since theIDT electrodes are sealed in the SAW device so as not to contact thecover, it is possible to secure predetermined operations.

In addition, in the above aspect of the invention, the space between theSAW chip and the cover in the bonded state may be equal to the thicknessof the IDT electrodes. Therefore, since the gap between the upper endsof the IDT electrodes and the lower surface of the cover can be removedby contacting the upper ends of the IDT electrodes and the lower surfaceof the cover, the thickness of the SAW device can be reduced down to aminimum thickness.

In addition, since the spaces between the alternate finger electrodesconstituting the IDT are closed by the lower surface of the cover,extrinsic material such as metal debris cannot penetrate into thespaces, so that it is possible to prevent short-circuiting between thealternate finger electrodes. As a result, it is possible to improvestability and reliability of operations and frequency, and it ispossible to improve high frequency performance of the SAW device byfurther reducing the spaces between the alternate finger electrodes.

In addition, in the above aspect of the invention, the cover may furthercomprise concave portions disposed at positions at least partiallyoverlapping with the external electrodes on the upper surface of thecover. Therefore, since conductive adhesive such as a solder paste usedto mount the SAW resonator on a print board or the like can penetrateinto the concave portions, the adhesion area can increase. AS a result,although the SAW device is manufactured with a small size and a thinthickness, it is possible to secure a sufficient mechanical strengthafter the mounting thereof.

In addition, in the above aspect of the invention, the concave portionsmay be disposed at outer peripheral edges of the cover. As a result, theSAW device can be supported by the side surfaces at the time of themounting thereof, so that it is possible to further improve the bondedstate and the mechanical strength.

In addition, the concave portions may be coated with metal films.Therefore, since wettability to the concave portions can be improved, aconductive adhesive such as a solder paste can easily penetrate into theconcave portions, and surface areas of the external electrodes canincrease practically. As a result, it is possible to improve theelectrical connection to the print board on which the SAW device ismounted.

In addition, in the above aspect of the invention, inner circumferentialsurfaces of the through-holes of the cover may be coated with metalfilms made of the conductive materials. As a result, the IDT electrodesand the external electrodes can be electrically connected to each other.

In addition, in the above aspect of the invention, the metal bondingportion and the extraction electrodes of the SAW chip may be constructedwith a Cr/Au film, and the metal bonding portion and the connectionelectrodes of the cover may be constructed with a Cr/Au film. As aresult, theses components can be bonded with a thermal bonding process.In addition, in the above aspect of the invention, the metal bondingportion and the connection electrodes of the cover may have an AuSnalloy film disposed on the Cr/Au film. As a result, the SAW chip and thecover can be bonded with a thermal pressing process or a eutecticbonding process. In any case, since the surface of the Cr/Au film of theextraction electrodes is not oxidized due to air contact (unlike an Alfilm), it is possible to secure electrical conduction to the connectionelectrode.

According to another aspect of the invention, there is provided a methodof manufacturing a surface acoustic wave device comprising the steps of:forming a SAW chip having IDT electrodes disposed on a main surface of apiezoelectric substrate, extraction electrodes extracted from the IDTelectrodes, and a metal bonding portion disposed along the entireperiphery of the main surface of the piezoelectric substrate; forming acover having through-holes disposed on an insulating substrate atpositions corresponding to the extraction electrodes of the SAW chip, ametal bonding portion disposed along the entire periphery of a lowersurface of the insulating substrate, and connection electrodes disposedon the lower surface of the insulating substrate along circumferences ofopenings of the through-holes; bonding the SAW chip and the cover in abody by bonding the metal bonding portion of the SAW chip and the metalbonding portion of the cover and bonding the extraction electrodes ofthe SAW chip and the connection electrodes of the cover so as tohermetically seal the IDT electrodes within a space defined between theSAW chip and the cover; forming external electrodes in peripheries ofopenings of the through-holes on an upper surface of the cover; andforming conductive materials in the through-holes and electricallyconnecting the IDT electrodes and the external electrodes.

By doing so, it is possible to implement a small-sized thin product, tosecure electrical conduction between the IDT electrodes and the externalelectrodes, and to hermetically seal the interior of the SAW device. Asa result, it is possible to manufacture a double-layered SAW devicecapable of improving the stability of operations and frequencycharacteristics.

In the above aspect of the invention, the method may further comprise astep of forming concave portions at positions at least partiallyoverlapping with the external electrodes on the upper surface of thecover. It is preferable that the concave portions on the upper surfaceof the cover are formed by using the same process as the process forforming the through-holes of the cover. As a result, by using themanufacturing process in the related art, it is possible to manufacturea SAW device having a good bonded state and high mechanical strengthafter the mounting thereof without increasing the number of processes.

In the above aspect of the invention, the IDT electrodes and theexternal electrodes may be electrically connected to each other byforming metal films made of the conductive materials on innercircumferential surfaces of the through-holes. Since the inner surfacesof the through-holes are constructed with metal films to improve thewettability thereto, conductive materials can be easily filled therein.As a result, it is possible to improve the reliability of the electricalconduction between the IDT electrodes and the external electrodes andthe hermetic sealing of the through-holes.

In the above aspect of the invention, the method may further comprise,after the SAW chip and the cover are bonded in a body, a step ofpolishing a surface of the -SAW chip and/or the cover. As a result, evenin a case where it is difficult to form a thin SAW chip or cover inadvance, it is possible to yield a thin SAW device.

In the above aspect of the invention, the metal bonding portion and theextraction electrodes of the SAW chip may be formed with a Cr/Au film,the metal bonding portion and the connection electrodes of the cover maybe formed with a Cr/Au film, and the metal bonding portion and theextraction electrodes of the SAW chip and the metal bonding portion andthe connection electrodes of the cover may be bonded with a thermalpressing process.

In the above aspect of the invention, the metal bonding portion and theextraction electrodes of the SAW chip may be formed with a Cr/Au film,the metal bonding portion and the connection electrodes of the cover maybe formed with a Cr/Au film and an AuSn alloy film thereon, and themetal bonding portion and the extraction electrodes of the SAW chip andthe metal bonding portion and the connection electrodes of the cover maybe bonded with a thermal pressing process or a eutectic bonding process.In any case, the surface of the Cr/Au film is not naturally oxidized dueto air contact unlike an Al film, and the Al film is formed later thanthe Cr/Au film. As a result, although the surface thereof is oxidizeddue to air contact, the electrical conduction between the extractionelectrodes and the connection electrode does not deteriorate.

In the above aspect of the invention, the method may further comprisethe steps of: forming a SAW chip wafer on which a plurality of the SAWchips are continuously disposed in the step of forming the SAW chip;forming a cover wafer on which a plurality of the covers arecontinuously disposed in the step of forming the cover; bonding the SAWchip wafer and the cover wafer in a body to form a wafer stackedstructure by bonding the metal bonding portions of the SAW chips of theSAW chip wafer and the metal bonding portions of the covers of the coverwafer and bond the extraction electrodes of the SAW chips and theconnection electrodes of the covers in the step of bonding the SAW chipand the cover in a body; and dicing the wafer stacked structure intoindividual SAW devices. As a result, since a plurality of the SAWdevices can be simultaneously manufactured, it is possible to improvemass productivity.

According to still another aspect of the invention, there is provided anIC card with the aforementioned surface acoustic wave device builttherein. As a result, it is possible to implement a desired thin ICcard.

According to still further another aspect of the invention, there isprovided a mobile electronic apparatus with the aforementioned surfaceacoustic wave device built therein. As a result, it is possible toimplement a much thinner mobile electronic apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1A is a plan view showing a SAW resonator according to a firstembodiment of the invention, and FIG. 1B is a cross sectional view takenalong line I-I of FIG. 1A.

FIG. 2 is a plan view showing a SAW chip of FIGS. 1A and 1B.

FIG. 3 is a bottom view showing a bonding surface of a cover of FIGS. 1Aand 1B.

FIGS. 4A to 4D are partially enlarged cross sectional views of a quartzwafer and a glass wafer for explaining a sequence of processes of amethod of manufacturing the SAW of FIG. 1.

FIG. 5A is a plan view showing a SAW resonator according to a secondembodiment of the invention, and FIG. 5B is a cross sectional view takenalong line V-V of FIG. 5A.

FIG. 6 is a plan view showing a SAW chip of FIGS. 5A and 5B.

FIG. 7 is a bottom view showing a bonding surface of a cover of FIGS. 5Aand 5B.

FIG. 8 is a partially enlarged cross sectional view showing a SAWresonator according to a modified example of the second embodiment.

FIGS. 9A to 9D are partially enlarged cross sectional views of a quartzwafer and a glass wafer for explaining a sequence of processes of amethod of manufacturing the SAW of FIG. 5.

FIG. 10A is a plan view showing a SAW resonator according to a modifiedexample of the first embodiment, and FIG. 10B is a side view thereof.

FIG. 11 is a plan view of a SAW resonator having a foot patterndifferent from that of FIGS. 10A and 10B.

FIG. 12 is a plan view of a SAW resonator in which concave portionshaving a pattern different from that of FIGS. 10A and 10B are disposed.

FIG. 13 is a plan view of a SAW resonator in which concave portionshaving another pattern different from that of FIGS. 10A and 10B aredisposed.

FIG. 14 is a plan view of a SAW resonator in which concave portionshaving still another pattern different from that of FIGS. 10A and 10Bare disposed.

FIG. 15A is a plan view showing a state where concave portions areformed on a glass wafer in a process for manufacturing the SAW resonatorof FIGS. 10A and 10B, and FIG. 15B is a plan view showing a state wherean electrode film for external electrodes is further formed.

FIG. 16A is a plan view showing a state where concave portions areformed on a glass wafer in a process for manufacturing the SAW resonatorof FIG. 12, and FIG. 16B is a plan view showing a state where anelectrode film for external electrodes is further formed.

FIGS. 17A and 17B are cross sectional views of a quartz wafer and aglass wafer for explaining an individualizing process using dicing in aprocess for manufacturing the SAW resonator of FIG. 12.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. In theaccompanying drawings, like reference numerals denote like elements.

FIGS. 1A and 1B show a SAW resonator according to a first embodiment ofthe invention. The SAW resonator 1 has a structure wherein a SAW chip 2and a cover 3 are directly bonded. As shown in FIGS. 1B and 2, the SAWchip 2 is constructed with a rectangular piezoelectric substrate 4, anIDT 5 constructed with a pair of alternate finger electrodes is formedon a central region of an upper surface thereof, and reflectors 6 and 6are formed at both longitudinal sides of the IDT. Lead wires 7 and 7 areextracted from bus bars of the alternate finger electrodes in the-opposite directions along longitudinal edges of the piezoelectricsubstrate 4, and the alternate finger electrodes are connected toextraction electrodes 8 and 8 which are formed approximately at (in thevicinities of) diagonal corner portions of the piezoelectric substrate.A metal. bonding portion 9 is formed along the entire circumference of aperipheral portion of the piezoelectric substrate 4.

Although the piezoelectric substrate 4 is made of quartz in theembodiment, other piezoelectric materials such as lithium, tantalate,and lithium niobate may be used. Although the alternate fingerelectrodes, the reflectors, and lead wires are constructed with an Alfilm in terms of characteristics, workability, and cost, otherconductive metal materials such as an aluminum alloy which are generallyused may be used. The extraction electrodes 8 and 8 and the metalbonding portion 9 are constructed with a Cr/Au film or a Cr/Ni/Au filmat the same height.

The cover 3 is constructed with a rectangular glass substrate 10, andtapered through-holes 11 and 11 converging from an upper surface to alower surface thereof are formed. The through-holes 11 and 11 aredisposed in the diagonal direction to correspond to the extractionelectrodes 8 and 8 of the SAW chip 2, so that it is possible to reducean outer dimension and to easily secure a pitch dimension of thethrough-holes. As shown in FIG. 3, on the lower surface of the glasssubstrate 10, connection electrodes 12 and 12 having a shapecorresponding to the extraction electrodes 8 and 8 of the SAW chip 2 areformed over the entire circumferences of the opening peripheries of thethough-holes. In addition, a metal bonding portion 13 is formed on thelower surface of the glass substrate 10 along the entire circumferenceof a peripheral portion thereof. The through-holes 11 and 11 and innercircumferential surfaces of the connection electrodes 12 and 12 whichare continuous with the through-holes are coated with metal films 14 and14 made of a conductive material. On the upper surface of the glasssubstrate 10, external electrodes 15 and 15 are formed in the openingperipheries of the through-holes. The external electrodes 15 and 15 areelectrically connected to the corresponding connection electrodes 12 and12 through the metal films 14 and 14 of the through-holes adjacent tothe external electrodes.

In the embodiment, the glass substrate 10 is made of soda glass having athermal expansion coefficient which is close to that of the quartz ofthe piezoelectric substrate 4. The connection electrodes 12 and 12 andthe metal bonding portion 13 are constructed with a Cr/Au film or aCr/Ni/Au film at substantially the same height. Similarly, the metalfilms 14 and 14 and the external electrodes 15 and 15 are constructedwith a Cr/Au film or a Cr/Ni/Au film.

In an alternative embodiment, the cover 3 may be made of other glassmaterials or insulating materials having a thermal expansion coefficientwhich is equal to or approximate to that of quartz or the quartz whichis the same as that of the piezoelectric substrate 4. In addition, in acase where the piezoelectric substrate 4 is made of a piezoelectricmaterial other than quartz, the cover 3 may be constructed with a thinplate made of an insulating material having a thermal expansioncoefficient which is equal to or approximate to that of thepiezoelectric material.

The SAW chip 2 and the cover 3 are bonded in a body by thermallypressing the metal bonding portion 9 and the metal bonding portion 13and thermally pressing the extraction electrodes 8 and 8 and theconnection electrodes 12 and 12, and the IDT 5 and the reflectors 6 and6 are hermetically sealed within a space defined between the SAW chip 2and the cover 3. In the embodiment, the thicknesses of the extractionelectrodes, the connection electrodes, and metal bonding portions 9 and13 are determined so that a thickness in the bonded states thereof arelarger than a thickness of the Al film. As a result, gaps are definedbetween the upper ends of the IDT and the reflectors and the lowersurface of the cover 3, so that the IDT and the reflectors do notcontact the cover 3. Accordingly, it is possible to ensure predeterminedexcitation and reception operations of the SAW.

The alternate finger electrodes of the IDT 5 are electrically connectedto the corresponding external electrodes 15 and 15 through theextraction electrodes 8 and 8 and the connection electrodes 12 and 12bonded thereto. The through-holes 11 and 11 are filled with sealingmembers 16 made of a conductive material, so that it is possible tosurely improve the reliability of the electrical conduction between theextraction and connection electrodes and the external electrodes and thehermetic sealing of the through-holes. As the conductive material of thesealing members 16, for example, AuSn, AuGe, a solder material, or ahigh temperature solder may be used.

In an alternative embodiment, the SAW chip 2 and the cover 3 can bebonded in a similar manner by forming an AuSn alloy film on the Cr/Aufilm of the connection electrodes 12 and 12 and the metal bondingportion 13 and performing a thermal pressing process or a eutecticbonding process.

Now, processes for manufacturing the SAW resonator of FIGS. 1A and 1B ina method according to the invention will be described with reference toFIGS. 4A to 4D. First, a large-sized SAW chip quartz wafer 21 in which aplurality of the SAW chips 2 of FIG. 2 are continuously disposed intransverse and longitudinal directions is prepared. In the quartz wafer21, a Cr/Au film having a predetermined thickness is formed on a surfaceof a quartz wafer plate piece, and the extraction electrodes 8 and themetal bonding portions 9 of each SAW chip are formed in desired patternsby using a photolithography technique. Next, an Al film having apredetermined thickness is formed on the surface of the quartz waferplate piece, and the IDT 5, the reflectors 6, and the lead wires 7 ofeach SAW chip are formed in desired patterns and so as to electricallyconnect the lead wires to the extraction electrodes 8 by using aphotolithography technique, similarly. In addition, the IDT, thereflectors and the lead wires may be formed in desired pattern films bydepositing aluminum. In the embodiment, since the Al film is formedlater on, although an oxide film is formed on a surface thereof due toair contact, the electrical conduction to the extraction electrodes 8constructed with the Cr/Au film in advance does not deteriorate.

In addition, a large-size cover glass wafer 22 in which a plurality ofthe covers 3 of FIG. 3 are continuously disposed in transverse andlongitudinal directions is prepared. In the glass wafer 22, thethough-holes 11 of each cover are formed on each glass plate piece byperforming, for example, a sand blasting process or an etching process.In particular, by using the sand blasting process, it is possible toeasily form the through-holes in a desired tapered shape. Next, a Cr/Aufilm having a predetermined thickness is formed on a lower surface ofthe glass plate piece, that is, a bonding surface for the SAW chip, andthe connection electrodes 12 and the metal bonding portions 13 of eachcover are formed in desired patterns by using a photolithographytechnique.

As shown in FIG. 4A, the quartz wafer 21 and the glass wafer 22 arealigned in up/down directions. As shown in FIG. 4B, the metal bondingportions 9 and the metal bonding portions 13 are contacted to overlapwith each other, and the extraction electrodes 8 and the connectionelectrodes 12 are contacted to overlap with each other. In this state,the wafers 21 and 22 are pressed and heated with a thermal pressingprocess using a commercially available bonding apparatus to be bonded ina body. As a result, the IDT 5 and the reflectors 6 are hermeticallysealed within a space between the SAW chip 2 and the cover 3. In analternative embodiment, in a process for forming the glass wafer 22, anAuSn alloy film is formed on the Cr/Au film of the connection electrodes12 and the metal bonding portions 13, and similarly, in the aligned andoverlapped state thereof, the wafers may be bonded in a body byperforming a thermal pressing process or a eutectic bonding process.

Next, in the embodiment, an upper surface of the wafer stacked structurewhich is formed in the above bonding process, that is, a surface of thecover 3 is uniformly polished down to a height denoted by virtual line23 in FIG. 4B (see FIG. 4C). The polishing process may be performed byusing well-known methods such as grinding and lapping. In the waferstacked structure, since the bonding between the extraction electrodes 8and the connection electrodes 12 as well as the bonding between themetal bonding portions 9 and 13 along the peripheries of the SAWresonators are strong, sufficient strength to the polishing process canbe obtained. As a result, the height of the resultant SAW resonator canbe reduced, so that it is possible to implement a desired thin product.This is advantageous in a case where it is difficult to form the glasswafer 22 having a thickness corresponding to a desired thickness of thecover 3 in terms of workability of the glass plate piece. The polishingprocess may be omitted in a case where a glass wafer having a desiredthickness can be prepared.

After the wafer stacked structure is rinsed, metal films 14 are formedon inner circumferential surfaces of the through-holes 11 and theconnection electrodes 12 by forming a Cr film and an Au film (or a Crfilm, an Ni film, and an Au film) with, for example, a sputteringprocess. Since the through-holes 11 are formed in a tapered shape asdescribed above, it is possible to easily perform the sputtering processon the meal films 14 from the upper surface of the wafer stackedstructure. In addition, similarly, on the upper surface of the waferstacked structure, that is, the upper surface of the cover 3, theexternal electrodes 15 constructed with a Cr/Au film (or a Cr/Ni/Aufilm) are formed in desired patterns (see FIG. 4D). The metal films 14and the external electrodes 15 may be simultaneously formed by using thesputtering process.

Next, the through-holes 11 are filled with the conductive material toform the sealing members 16. Since the wettability of the innercircumferential surfaces of the through-holes 11 to the conductivematerial is improved due to the metal films 14 formed in advance, it ispossible to easily perform the filling of the sealing members 16. As aresult, it is possible to surely improve the reliability of theelectrical conduction through the connection electrodes and extractionelectrodes between the alternate finger electrodes of the IDT 5 and thecorresponding external electrodes 15 and the hermetic sealing of thethrough-holes. Finally, an individualizing process is performed bydicing the wafer stacked structure along the outlines 24 of the SAWresonators which are perpendicular to each other in transverse andlongitudinal directions. As a result, the quartz oscillator 1 shown inFIGS. 1A and 1B is provided.

In an alternative embodiment, the glass wafer 22 is formed to allow thecover 3 to have other frequency adjusting through-holes (not shown). Thefrequency can be adjusted by externally performing dry etching on SAWchip quartz planes of the individualized SAW resonators through thefrequency adjusting through-holes. The frequency-adjusted SAW resonatorsare disposed in a vacuum, and the frequency adjusting through-holes arehermetically closed by fusing, for example, a low melting point metalmaterial. In this case, in order to improve wettability, it ispreferable that metal films made of a conductive material are formed oninner surfaces of the frequency adjusting through-holes in advance.

FIGS. 5A and 5B show a SAW resonator according to a second embodiment ofthe invention. Similarly to the first embodiment in FIGS. 1A and 1B, theSAW resonator 1 according to the embodiment has a structure where a SAWchip 2 and a cover 3 are directly bonded. As shown in FIGS. 5B and 6,the SAW chip 2 includes an IDT 5 constructed with a pair of alternatefinger electrodes formed on a central region of an upper surface of apiezoelectric substrate 4 made of quartz or the like, reflectors 6 and 6disposed at both longitudinal sides of the IDT, lead wires 7 and 7extracted from bus bars of the alternate finger electrodes, extractionelectrodes 8 and 8 formed at vicinities of diagonal corner portions ofthe piezoelectric substrate, and a metal bonding portion 9 formed alongthe entire peripheral portion of the piezoelectric substrate 4.

In the cover 3 constructed with a rectangular glass substrate 10,through-holes 11 and 11 having a tapered shape converging from an uppersurface to a lower surface thereof are disposed in the diagonaldirection to correspond to the extraction electrodes 8 and 8 of the SAWchip 2. As shown in FIG. 7, on the lower surface of the cover 3,connection electrodes 12 and 12 corresponding to the extractionelectrodes 8 and 8 are formed on the opening peripheries of thethough-holes, and a metal bonding portion 13 is formed along the entireperipheral portion thereof. In addition, the through-holes 11 and 11 andinner circumferential surfaces of the connection electrodes 12 and 12are coated with metal films 14 and 14 made of a conductive material. Onthe upper surface of the cover 3, external electrodes 15 and 15 areformed in the opening peripheries of the through-holes and electricallyconnected to the connection electrodes 12 and 12 through the metal films14 and 14 of the through-holes adjacent to the external electrodes.

Similarly to the first embodiment, the SAW chip 2 and the cover 3 arebonded in a body by, for example, thermally pressing the metal bondingportion 9 and the metal bonding portion 13 and thermally pressing theextraction electrodes 8 and 8 and the connection electrodes 12 and 12.In an alternative embodiment, the SAW chip 2 and the cover 3 can bebonded by forming an AuSn alloy film on a Cr/Au film of the connectionelectrodes 12 and 12 and the metal bonding portion 13 and performing athermal pressing process or a eutectic bonding process. Thethrough-holes 11 and 11 are filled with sealing members 16 made of aconductive material such as AuSn, AuGe, a solder material, and a hightemperature solder, so that it is possible to surely improve thereliability of the electrical conduction between the extraction andconnection electrodes and the external electrodes and the hermeticsealing of the through-holes.

In the embodiment, the IDT 5, the reflectors 6 and 6, and the lead wires7 and 7 are hermetically sealed within a space defined between the SAWchip 2 and the cover 3 by directly contacting the upper end of the SAWchip 2 and the lower surface of the cover 3. As a result, thicknesses t1of the metal bonding portion 9 and the extraction electrodes 8 andthicknesses t2 of the metal bonding portion 13 and the connectionelectrodes 12 are determined so that a thickness t1+t2 in the bondedstate thereof is equal to a thickness T1 of the Al film which the IDT 5,the reflectors 6 and 6, or the like are constructed with.

As a result, the gaps between the IDT 5 or the like of the SAW chip andthe lower surface of the cover 3 are removed, so that the thickness ofthe SAW resonator 1 can be reduced down to a minimum thickness. Inaddition, since the spaces between the alternate finger electrodesconstituting the IDT are closed by the lower surface of the cover 3,extrinsic material such as metal debris cannot penetrate into thespaces, so that it is possible to prevent short-circuiting between thealternate finger electrodes. In addition, it is clarified by theinventors that, although the IDT 5 and the cover 3 are contacted to eachother, there is no substantial change in a resonance frequency or a CIvalue, and the characteristics of at least a practical SAW resonator 1are not influenced.

FIG. 8 shows a modified example of the SAW resonator according to thesecond embodiment. In the SAW resonator 1 according to the modifiedexample, each of the alternative finger electrodes of the IDT 5 formedon the upper surface of the SAW chips 2 are constructed with an Al filmand a protective film 17 made of alumina coated on the Al film. In thiscase,. the thickness of the IDT 5, that is, a total thickness T1+T2 of athickness T1 of the Al film and the a thickness T2 of the protectivefilm 17 are determined so as to be equal to the thickness t1+t2 of thebonded state of the metal bonding portion 9 and extraction electrodes 8and of the metal bonding portion 13 and the connection electrodes 12.The protective film 17 may be formed by, for example, performing apositive electrode oxidation process on a surface of the Al film formedon the SAW chip 2.

By doing so, similarly to the embodiment shown in FIGS. 5A and 5B, theIDT 5, the reflectors 6 and 6, and the lead wires 7 and 7 arehermetically sealed within a space defined between the SAW chip 2 andthe cover 3 in a state of directly contacting the upper end of the ITD 5and the lower surface of the cover 3. As such, since the alternatefinger electrodes of the IDT 5 are coated with the protective film 17,although the cover 3 exerts some pressure on the IDT 5, the influence ofthe pressure on the operation of the SAW resonator 1 can be more surelyeliminated or alleviated.

Now, processes for manufacturing the SAW resonator of FIGS. 5A and 5Bwill be described with reference to FIGS. 9A to 9D, similarly to theembodiment shown in FIGS. 4A to 4D. First, a large-sized SAW chip quartzwafer 21 in which a plurality of the SAW chips 2 of FIG. 6 arecontinuously disposed in transverse and longitudinal directions isprepared. In the quartz wafer 21, a Cr/Au film having a predeterminedthickness t1′ is formed on a surface of a quartz wafer plate piece, andthe extraction electrodes 8 and the metal bonding portions 9 of each SAWchip are formed in desired patterns by using a photolithographytechnique. Next, an Al film having a predetermined thickness T1 isformed on the surface of the quartz wafer plate piece, and the IDT 5,the reflectors 6, and the lead wires 7 of each SAW chip are formed indesired patterns and so as to electrically connect the lead wires to theextraction electrodes 8 by using a photolithography technique,similarly. Since the Al film is formed later on, although an oxide filmis formed on a surface thereof due to air contact, the electricalconduction to the extraction electrodes 8 constructed with the Cr/Aufilm in advance does not deteriorate.

In an alternative embodiment, the IDT, the reflectors and the lead wiresmay be formed in desired pattern films and thicknesses by depositingaluminum. In addition, in a case where the SAW resonator according tothe modified example shown in FIG. 8, the quartz wafer 21 ismanufactured so that the IDT 5 of each of the SAW chips is coated withthe protective film 17. The protective film 17 may be formed by, forexample, performing a positive electrode oxidation process on the Alfilm formed on the quartz wafer plate piece. In this case, the thicknessT2 of the protective film 17 can be controlled to be a desired thicknessby adjusting conditions of the positive oxidation process.

In addition, a large-sized cover glass wafer 22 in which a plurality ofthe covers 3 of FIG. 7 are continuously disposed in transverse andlongitudinal directions is prepared. In the glass wafer 22, thethough-holes 11 of each cover are formed on each glass plate piece byperforming, for example, a sand blasting process or an etching process.In particular, by using the sand blasting process, it is possible toeasily form the through-holes in a desired tapered shape. Next, a Cr/Aufilm having a predetermined thickness t2′ is formed on a lower surfaceof the glass plate piece, that is, a bonding surface for the SAW chip,and the connection electrodes 12 and the metal bonding portions 13 ofeach cover are formed in desired patterns by using a photolithographytechnique.

As shown in FIG. 9A, the quartz wafer 21 and the glass wafer 22 arealigned in up/down directions. As shown in FIG. 9B, the metal bondingportions 9 and the metal bonding portions 13 are contacted to overlapwith each other, and the extraction electrodes 8 and the connectionelectrodes 12 are contacted to overlap with each other. By taking intoconsideration a decrease in the thicknesses of the metal films duringthe bonding, it is preferable that the thicknesses t1′ of the extractionelectrodes 8 and the metal bonding portions 9 of the quartz wafer 21 andthe thicknesses t2′ of the connection electrodes 12 and the metalbonding portions 13 of the quartz wafer 22 are determined so that atotal thickness t1′+t2′ thereof is slightly larger than a thicknesst1+t2=T1 in the bonded state.

In the state that the wafers 21 and 22 are overlapped with each other,the wafers 21 and 22 are pressed and heated with a thermal pressingprocess using a commercially available bonding apparatus to be bonded ina body. The pressing is performed to exert the pressure from the uppersurface of the glass wafer 22 uniformly on the entire surface thereof,so that the upper ends of the IDT 5, the reflectors 6 and 6 and the leadwires 7 and 7 contact the lower surface of the cover 3. As a result, theIDT 5, the reflectors 6 and 6, and the like are hermetically sealedwithin a space defined between the SAW chip 2 and the cover 3. In analternative embodiment, in a process for forming the glass wafer 22, anAuSn alloy film is formed on the Cr/Au film of the connection electrodes12 and the metal bonding portions 13, and similarly, in the aligned andoverlapped state thereof, the wafers may be bonded in a body byperforming a thermal pressing process or a eutectic bonding process.

According to the embodiment, the gaps between the IDT 5 or the like ofthe SAW chip and the lower surface of the cover 3 are removed, so thatthe thickness of the SAW resonator 1 can be reduced down to a minimumthickness. In addition, since the spaces between the alternate fingerelectrodes constituting the IDT are closed by the lower surface of thecover 3, extrinsic material such as metal debris generated during thefollowing processes cannot penetrate into the spaces, so that it ispossible to prevent short-circuiting between the alternate fingerelectrodes.

Next, an upper surface of the wafer stacked structure which is formed inthe above bonding process, that is, a surface of the cover 3 isuniformly polished down to a height denoted by virtual line 23 of FIG.9B (see FIG. 9C), and the height of the resultant SAW resonator can bereduced, so that it is possible to implement a desired thin product. Thepolishing process may be omitted in a case where a glass wafer having adesired thickness can be prepared.

After the polished wafer stacked structure is rinsed, metal films 14 areformed on inner circumferential surfaces of the through-holes 11 and theconnection electrodes 12 by forming a Cr film and an Au film (or a Crfilm, an Ni film, and an Au film) with, for example, a sputteringprocess. In addition, similarly, on the upper surface of the waferstacked structure, that is, the upper surface of the cover 3, theexternal electrodes 15 constructed with a Cr/Au film (or a Cr/Ni/Aufilm) are formed in desired patterns (see FIG. 9D).

Next, the through-holes 11 are filled with the conductive material toform the sealing members 16. As a result, it is possible to surelyimprove the reliability of the electrical conduction through theconnection electrodes and extraction electrodes between the alternatefinger electrodes of the IDT 5 and the corresponding external electrodes15 and the hermetic sealing of the through-holes. Finally, aninitializing process is performed by dicing the wafer stacked structurealong outlines 24 of the SAW resonators which are perpendicular to eachother in transverse and longitudinal directions. As a result, the quartzoscillator 1 shown in FIGS. 5A and 5B is provided.

In an alternative embodiment, a glass wafer 22 is formed to allow acover 3 to have other frequency adjusting through-holes (not shown), andthe frequency can be adjusted by externally performing dry etching onSAW chip quartz planes of the individualized SAW resonators through thefrequency adjusting through-holes. After adjusting the frequency, thefrequency adjusting through-holes are hermetically closed by fusing, forexample, a low melting point metal material in a vacuum.

FIGS. 10A and 10B show a modified example of the SAW resonator 1 ofFIGS. 1A and 1B. Concave portions 18 having a substantially quadrantcircle shape are formed at the corner portions on an upper surface ofthe covers 3 where the though-holes 11 and external electrodes 15 atopening peripheries thereof are formed. In the embodiment, the externalelectrodes 15 are formed on the entire upper surface excluding alongitudinal central region of the glass substrate 10, and the concaveportions 18 are formed to overlap with the external electrodes 15. As aresult, since conductive adhesive such as a solder paste used to mountthe SAW resonator 1 on a surface of a print board or the like can deeplypenetrate into the concave portions 18, the adhesion area can increase,and the SAW resonator 1 can be supported by the side surfaces thereof.Accordingly, a good adhesive state can be obtained, and a mechanicalstrength against bending after mounting can be improved. In addition, byproviding the concave portions 18 to the corner portions of the cover 3,careless breakage of the corner portions of the cover 3 made of afragile material such as glass in the embodiment can be prevented, sothat it is possible to improve handling workability.

In the embodiment, metal films 19 are coated on the inner surface of theconcave portions 18 so as to form side surface electrodes connected tothe external electrodes 15. As a result, it is possible to improve thewettability to conductive adhesive used to mount the SAW resonator 1 ona print board (not shown) or the like, so that adhesiveness can beimproved. In addition, the areas of the external electrodes 15 aresubstantially enlarged, so that the electrical connection performancecan be improved. In addition, the side surface electrodes are not formedon the entire thickness of the glass substrate 10, but the sideelectrodes are limitedly formed within the concave portions 18, so thatit is possible to suitably prevent electrical short-circuiting betweenthe SAW chip 2 and cover 3 and the bonding films 9 and 13. In addition,although the problem of electrical short-circuiting can be prevented byusing a resin material for the bonding films, other problems inreliability such as insufficient water resistance may occur.

The shape and array, that is, a foot print of the external electrodes 15may be formed in various ones according to the number of the extractionelectrodes or the like, as needed. FIG. 11 shows an example where thenumber of the external electrodes 15 is four instead of two as in FIGS.10A and 10B, and in other words, each of the external electrodes 15 ofFIGS. 10A and 10B is divided into two in a width direction. In addition,in the embodiment, the concave portions 18 are formed in a shape of alarge groove which is elongated from each of the corner portions of thecover 3 along each of the longitudinal edges. Similarly, since theadhesion area can increase due to the concave portions 18, a goodadhesive state can be obtained, and a mechanical strength againstbending after the mounting can be improved. In addition, breakage of thecorner portions of the covers 3 is prevented, and in a case where theinner portions thereof are coated with the metal films, the wettabilityto the conductive adhesive and electrical connection performance can beimproved.

FIGS. 12 to 14 shows concave portions 18 having various shapes and arraypatterns in a SAW resonator 1 similar to that shown in FIGS. 10A and10B. Referring to FIG. 12, the concave portions 18 may be formed in ashape of step differences having a predetermined width along an entirecircumferential edge of an upper surface of the cover 3. Referring toFIG. 13, the concave portions 18 may be formed with a plurality ofstraight line shaped grooves which extend parallel to each other in aslanted direction on an upper surface of the cover 3. In the embodimentshown in the figure, the grooves for the concave portions 18 aredisposed to traverse the through-holes 11. Referring to FIG. 14, theconcave portions 18 may be formed with a plurality of recesses which aredisposed relatively in random. However, the concave portions 18 are notlimited to the aforementioned shapes, but the concave portions 18 may beformed in various shapes such as a circle and ellipse. In addition, thecross section thereof may be determined from various shapes such as V,⊃, and U shapes.

The SAW resonator 1 according to the modified embodiment may bemanufacture by using the manufacturing processes described withreference to FIGS. 4A to 4D and 9A to 9D. FIGS. 15A and 15B shows theglass wafer 22 used to manufacture the SAW resonator 1 of FIGS. 10A and10B. As shown in FIG. 15A, in the process for forming the through-holes11 on an upper surface of the glass wafer 22, concave portions 20 havingthe shape of a circle are formed to correspond to the concave portions18 having the shape of a quadrant circle by using a blast process or anetching process. After the glass wafer 22 and the quartz wafer 21 onwhich the IDTs 5 or the like are formed are bonded in a body, externalelectrodes 15 are formed on an upper surface of the glass wafer 22, asshown in FIG. 15B. At the same time, metal films are formed on innercircumferential surfaces of the through-holes 11 and inner surfaces ofthe concave portions 20.

Finally, as shown in FIG. 16, an individualizing process is performed bydicing the wafer stacked structure along the outlines 24 of the SAWresonators which are perpendicular to each other in transverse andlongitudinal directions. The concave portions 20 desirably have a sizelarger than a width of the blade used for the dicing.

In an alternative embodiment, the concave portions 20 may be formed bydicing the surface of the glass wafer 22. This method is particularlysuitable to manufacture the SAW resonator 1 having straight line shapedconcave portions 18, as shown in FIG. 12. FIGS. 17A and 17B shows theglass wafer 22 used to manufacture the SAW resonator 1 of FIG. 12. Asshown in FIG. 17A, before or after the process for forming thethrough-holes 11 on an upper surface of the glass wafer 22, concaveportions 20 having wide straight line shaped grooves are formed tocorrespond to the concave portions 18 having straight line shapedgrooves by using a blast process or an etching process. The blade usedfor the groove forming process for the concave portions 20 has a widthlarger than that of the blade used for the individualizing process.

After the glass wafer 22 and the quartz wafer 21 on which the IDTs 5 orthe like are formed are bonded in a body, external electrodes 15 areformed on an upper surface of the glass wafer 22, as shown in FIG. 17B.At the same time, metal films are formed on inner circumferentialsurfaces of the through-holes 11 and inner surfaces of the concaveportions 20. Finally, an individualizing process is performed by dicingthe wafer stacked structure in transverse and longitudinal directionsalong the outlines 24 of the SAW resonators. Since the dicing forindividualization is performed along portions to which the thin grooveforming process of the concave portion 20 is performed, resistance tocutting is small, so that the cutting can be performed at a higherspeed.

Although the embodiments suitable for the present invention aredescribed in detail, the invention can be employed in various modifiedexamples of the embodiments. For example, the invention may be appliedto other SAW devices using a SAW element such as a filter and anoscillator. In addition, although only the glass wafer is polished inorder to implement a thin SAW device in the above embodiment, the quartzwafer or both the glass and quartz wafers may be polished in otherembodiments. In addition, the SAW device according to the invention maybe built into an IC card or a mobile electronic apparatus.

1. A surface acoustic wave device comprising: a surface acoustic wave(SAW) chip having: IDT electrodes disposed on a main surface of apiezoelectric substrate; extraction electrodes extracted from the IDTelectrodes; and a metal bonding portion disposed along an entireperiphery of the main surface of the piezoelectric substrate; and acover having: through-holes in an insulating substrate at positionscorresponding to the extraction electrodes of the SAW chip; a metalbonding portion disposed along an entire periphery of a lower surface ofthe insulating substrate; connection electrodes disposed on the lowersurface of the insulating substrate along circumferences of openings ofthe through-holes; and external electrodes disposed on an upper surfaceof the insulating substrate in peripheries of openings of thethrough-holes; wherein the SAW chip and the cover are bonded in a bodyby bonding the metal bonding portion of the SAW chip and the metalbonding portion of the cover and bonding the extraction electrodes ofthe SAW chip and the connection electrodes of the cover so as tohermetically seal the IDT electrodes within a space defined between theSAW chip and the cover, and wherein the IDT electrodes and the externalelectrodes are electrically connected to each other through conductivematerial in the through-holes.
 2. The surface acoustic wave deviceaccording to claim 1, wherein the space between the SAW chip and thecover in a bonded state is larger than a thickness of the IDT electrode.3. The surface acoustic wave device according to claim 1, wherein thespace between the SAW chip and the cover in a bonded state is equal to athickness of the IDT electrode.
 4. The surface acoustic wave deviceaccording to claim 1, wherein the cover further comprises concaveportions disposed at positions at least partially overlapping with theexternal electrodes on the upper surface of the cover.
 5. The surfaceacoustic wave device according to claim 4, wherein the concave portionsare disposed at outer peripheral edges of the cover.
 6. The surfaceacoustic wave device according to claim 4, wherein the concave portionsare coated with metal films.
 7. The surface acoustic wave deviceaccording to claim 1, wherein inner circumferential surfaces of thethrough-holes are coated with metal films made of the conductivematerial to electrically connect the IDT electrodes and the externalelectrodes.
 8. The surface acoustic wave device according to claim 1,wherein the metal bonding portion and the extraction electrodes of theSAW chip comprise a Cr/Au film, and the metal bonding portion and theconnection electrodes of the cover comprise a Cr/Au film.
 9. The surfaceacoustic wave device according to claim 8, wherein the metal bondingportion and the connection electrodes of the cover has an AuSn alloyfilm disposed on the Cr/Au film.
 10. A method of manufacturing a surfaceacoustic wave device comprising steps of: forming a SAW chip having: IDTelectrodes disposed on a main surface of a piezoelectric substrate;extraction electrodes extracted from the IDT electrodes; and a metalbonding portion disposed along the entire periphery of the main surfaceof the piezoelectric substrate; forming a cover having: through-holes inan insulating substrate at positions corresponding to the extractionelectrodes of the SAW chip; a metal bonding portion disposed along anentire periphery of a lower surface of the insulating substrate; andconnection electrodes disposed on the lower surface of the insulatingsubstrate along circumferences of openings of the through-holes; bondingthe SAW chip and the cover in a body by bonding the metal bondingportion of the SAW chip and the metal bonding portion of the cover andbonding the extraction electrodes of the SAW chip and the connectionelectrodes of the cover so as to hermetically seal the IDT electrodeswithin a space defined between the SAW chip and the cover; formingexternal electrodes in peripheries of openings of the through-holes onan upper surface of the cover; and forming conductive material in thethrough-holes and electrically connecting the IDT electrodes and theexternal electrodes.
 11. The method according to claim 10, furthercomprising a step of forming concave portions at positions at leastpartially overlapping with the external electrodes on the upper surfaceof the cover.
 12. The method according to claim 10, wherein the IDTelectrodes and the external electrodes are electrically connected toeach other by forming metal films made of the conductive material oninner circumferential surfaces of the through-holes.
 13. The methodaccording to claim 10, further comprising, after the SAW chip and thecover are bonded in a body, a step of polishing a surface of at leastone of the SAW chip and the cover.
 14. The method according to claim 10,wherein the metal bonding portion and the extraction electrodes of theSAW chip are formed with a Cr/Au film, the metal bonding portion and theconnection electrodes of the cover are formed with a Cr/Au film, and themetal bonding portion and the extraction electrodes of the SAW chip andthe metal bonding portion and the connection electrodes of the cover arebonded with a thermal pressing process.
 15. The method according toclaim 10, wherein the metal bonding portion and the extractionelectrodes of the SAW chip are formed with a Cr/Au film, the metalbonding portion and the connection electrodes of the cover are formedwith a Cr/Au film and an AuSn alloy film thereon, and the metal bondingportion and the extraction electrodes of the SAW chip and the metalbonding portion and the connection electrodes of the cover are bondedwith one of a thermal pressing process and a eutectic bonding process.16. The method according to claim 10, further comprising steps of:forming a SAW chip wafer on which a plurality of the SAW chips aresequentially disposed in the step of forming the SAW chip; forming acover wafer on which a plurality of the covers are sequentially disposedin the step of forming the cover; bonding the SAW chip wafer and thecover wafer in a body to form a wafer stacked structure by bonding themetal bonding portions of the SAW chips of the SAW chip wafer and themetal bonding portions of the covers of the cover wafer and bonding theextraction electrodes of the SAW chips and the connection electrodes ofthe covers in the step of bonding the SAW chip and the cover in a body;and dicing the wafer stacked structure into individual SAW devices. 17.An IC card having the surface acoustic wave device according to claim 1built therein.
 18. A mobile electronic apparatus having the surfaceacoustic wave device according to claim 1 built therein.